During the drilling, work over, or plug and abandonment of oil and gas producing wellbores, a variety of down hole tools may be attached to a pipe or coiled tubing string and utilized to perform various functions within the wellbore. Circumstances arise making it desirable to bypass flow around the downhole tool string within the wellbore. The toolstring is often referred to as a bottom hole assembly (BHA). These may consist of a variety of tools. Most frequently it will contain a downhole mud motor. These mud motors have a maximum flow rate rating which must not be exceeded otherwise damage to the mud motor will occur. Thus, if a flow rate is required by an operator which is in excess of the mud motor rating, a portion of the fluid being circulated must be bypassed or diverted to the wellbore. Other circumstances can include lost circulation where lost circulation material (LCM) must be pumped, well control issues, and others of the like which require the flow of fluid within the pipestring to be bypassed around the toolstring or BHA.
In many wells being drilled today, hydraulic fracturing is being utilized to maximize the output of the wells. Hydraulic fracturing, known as fracking, requires multiple stages to be perforated and fractured with a composite bridge plug set between each stage. These composite bridge plugs must be subsequently drilled out using a mud motor and drill bit. These mud motors have flow rate limitations which are oftentimes not high enough to properly clean the drilled debris (bridge plug parts) out of the wellbore. Thus a bypass valve apparatus must be utilized above the mud motor to divert a portion of the fluid being circulated directly into the wellbore and therefore avoiding exceeding the mud motor's flow rating.
There are currently two common types of bypass valves on the market. The first is known as a dual circulation sub (DCS) and can only be activated once with no means to deactivate. The DCS contains a piston which blocks fluid exit ports and is held in place via shear screws. A steel ball must be pumped from surface which lands and seals upon the piston. Pressure is then applied until the shear screws fail and the piston shifts downward, revealing the fluid exit ports. At this point, all fluid being circulated is directed into the wellbore. There is no means to reclose the fluid exit ports.
A second bypass valve device, (known as a PBL® Multiple Activation Bypass System), employs a deformable ball to activate the bypass valve, allowing fluid to travel into the wellbore and around the tool string. A second, metal ball(s) is employed to close the bypass valve off and allow circulation to continue through the tool string. This device allows the operator to perform this function several times while the device is in the wellbore. There are two main disadvantages to this process. The first is that the balls that are pumped down are captured in a “basket”, thus preventing further balls to be circulated to devices below this bypass device. This is very important as many downhole tools require ball activation. If two ball activated devices are run simultaneously, the uppermost device must utilize a larger ball for activation than the lower device. In this case, the PBL® disallows balls to continue through it once the first ball has been captured. The second disadvantage is that pumping a ball through a pipe or coiled tubing string is a very time consuming, and thus costly process, especially through a coiled tubing string where the ball must travel through the entire spool of coiled tubing before it even reaches the vertical column within the wellbore, and eventually land in the intended device.
Consequently, there is a need for a mechanically activated bypass valve apparatus which does not utilize any balls to either activate or deactivate and also has the ability for balls to be circulated through this device to activate other tools run lower in the toolstring.